The present invention relates generally to systems and methods for transmitting data. More specifically, the present invention relates to systems and methods for embedding compressed digital video data in a bitstream, potentially containing additional compressed digital video data of a different compression format, and transmitting the bitstream over communication channels.
Video services and programs are provided by a spectrum of different video content suppliers. For example, residential digital video services may include digital television, video OnDemand, Internet video, etc.—each service having hundreds of programs. A set-top box (STB) located in a residential home receives video services and programs from a number of different video content suppliers via assorted transmission channels. Transmission channels such as coaxial cable distribution networks, digital subscriber loop (DSL) access networks, ATM networks, satellite, or wireless digital transmission facilities are all well known. Preferably, all digital video programs provided by video content suppliers are available for all residential users.
Since transmission of video data with existing communication channels often requires excessive bandwidth, compression is an approach that has been used to make digital video images more transportable. Digital video compression formats allow digitized video frames to be represented digitally in much more efficient manner. Compression of digital video makes it practical to transmit the compressed signal using digital channels at a fraction of the bandwidth required to transmit the original signal without compression. There is an abundant number of proprietary and public video data compression formats currently in use. Popular proprietary video compression formats include the Microsoft streaming format, QuickTime, RealNetworks, etc. Public video data compression formats include numerous international standards built upon video data compression schemes such as MPEG-1, MPEG-2, MPEG-4, H.261, H.262, H.263, H.263+, wavelet, fractal, etc.
These standardized and proprietary compression formats rely on several algorithm schemes to compress the video data. The MPEG-2 standard, for example, includes motion compensated transform coding (for example, DCT transforms or wavelet/sub-band transforms), quantization of the transform coefficients, and variable length coding (VLC). The motion compensated encoding removes the temporally redundant information inherent in video sequences. The transform coding enables orthogonal spatial frequency representation of spatial domain video signals. Quantization of the transformed coefficients reduces the number of levels required to represent a given digitized video. The other factor contributing to the compression is the use of variable length coding (VLC) so that most frequently used symbols are represented by the shortest code word. In general, the number of bits used to represent a given image determines the quality of the decoded picture. The more bits used to represent a given image, the better the image quality.
A bitstream refers to a continuous sequence of binary bits used to digitally represent compressed video, audio or computer data. The system that is used to compress digitized video data in an uncompressed bitstream using a compression scheme is called an encoder or encoding apparatus. The system that is used to decompress a video bitstream using the reverse schemes is called a decoder or decoding apparatus. In the above example of a set-top box (STB) located in a residential home, the set-top box is typically installed with a static decoding capability. More specifically, the set-top box only decodes video content according to the video decompression formats that the set-top box hardware and software are initially configured to manage. Any video content outside of the established decoding capability of the set-top box results in inaccessible video content services and programs for the residential user. Video content and programs refer to compressed video data transmitted by a network source or supplier for reception, decompression and viewing by an end-user.
Currently, there is no synchronization between video content suppliers with respect to which video compression format is to be globally used. As the decompression capability of the residential user is typically static, the burden of facing the kaleidoscope of public and proprietary video compression formats must then be overcome at some point between the video content suppliers and the residential user. The decompression burden becomes more unruly when residential users carry different decoding capabilities. Different decoding capabilities are common when different local cable companies supplying the set-top boxes implement different decoding capabilities, or when a set-top box strictly includes proprietary decoding capabilities—at the expense of other proprietary and public decoding capabilities. Also, it is important to point out that compressed video bitstreams are usually generated by video content providers using either real-time encoders or pre-compressed video server storage systems. Both are likely to be in a remote site, away from the network and end-user. This increases the difficulty in encoding the video signal with a format suitable or tailored to the decoding capability of an end-user.
In addition to format incompatibility problems between video content suppliers and end-users, modern video service also includes multiple programs to be simultaneously received by the end-user. The multiple video programs may often be too large for the available bandwidth on the channels used to transmit the programs from the suppliers to the users. Overloading the available bandwidth may lead to degradation in transmission quality or unavailability of programs to end-users.
Based on the foregoing, it should be evident that there is a need for methods and systems of providing compressed digital video content over data channels that fit within the available bandwidth and that comply with an end-user's decoding capability.